The invention is in the field of electrical resistance heaters, especially heaters for tubes, pipes, or flexible hose. More particularly, the invention is directed to an electrical heater formed as a strip that is permanently set in the shape of a helix.
Electrical resistance heaters are commonly used in the art to heat conduits, such as tubes, hoses, and pipes. Such heaters typically are formed as flat strips that are wrapped around the tube or pipe to be heated. The strip comprises an electrical resistance heater, such as a wire or etched element, encapsulated in electrical insulation such as an elastomer or a suitably flexible plastic material. Silicone elastomer with or without fiberglass reinforcement is commonly used as an electrical insulation. In certain applications, the heater strip is helically wrapped around the circumference of the conduit. The heater is held in place with adhesive, or mechanical fasteners such as tie-wraps or hose clamps.
Though certainly safe and effective, these prior heaters have been found to be lacking in certain qualities. For example, applying a flat strip heater to a conduit having a curvature is difficult, which generally results in the heater poorly conforming to the conduit, especially if the curvature is complex. Air gaps often occur between the heater and the conduit, which significantly reduces efficiency of heat transfer from the heater to the conduit, and may cause local hot spots leading to premature failure. In certain applications, gaps are reduced by bonding the heater to the conduit, however, this approach renders the heater difficult to maintain and replace in the field. In addition, the final shape of an installed bendable conduit is often unknown before installation. A flat strip heater applied to a bendable conduit without bonding may develop gaps after the conduit is forced into a curvature upon installation of the conduit. Bonding the heater to a bendable conduit significantly reduces flexibility and the ability of the conduit to be conformed to a curvature. Therefore, an improved heater is desired that more readily conforms to a conduit having a curvature, especially a bendable conduit.